Liquid developer for electrophotography containing yellow pigment

ABSTRACT

WHEREIN R IS OCH3, OC2H5 OR OC3H7.   PHENYLENE)-R   1-YL CL-(1,2-PHENYLENE)-N=N-CH(-CO-CH3)-CO-NH-(1,4-   3-CL-4-(R-(1,4-PHENYLENE)-NH&#39;&#39;-CO-CH(-CO-CH3)-N=N)-BENZEN-   PHENYLENE)-R OR   1-YL CL-(1,2-PHENYLENE)-N=N-CH(-CO-CH3)-CO-NH-(1,2-   3-CL,4-(R-(1,2-PHENYLENE)-NH&#39;&#39;-CO-CH(-CO-CH3)-N=N)-BENZEN-   A LIQUID DEVELOPER FOR DEVELOPING A LATENT ELECTROSTATIC IMAGE CONTAINING AT LEAST ONE OF THE FOLLOWING:

US. Cl. 252-62.1 9 Claims ABSTRACT OF THE DHSCLOSURE A liquid developer for developing a latent electrostatic image containing at least one of the following:

R G1 I I II E wherein R is OCH OC H or OC H BACKGROUND OF THE INVENTION (1) Field of invention The present invention relates to a liquid developer for the development of a latent electrostatic image and, in particular, to a liquid developer containing yellow pigment which is positivel charged and which is especially suited for the reproduction of a multicolor image.

(2) Description of preferred embodiments Conventionally, when developing a latent electrostatic image formed by an electrostatic recording method, various developing methods have been employed. Such methods as liquid developing or electrophoretic developing are excellent in that they can produce high quality images and can faithfully reproduce continuous tone images. Where electrostatic latent images are formed repeatedly on a light-sensitive material such as an Electrofax paper, made by coating a photoconductive light-sensitive layer containing ZnO on a sheet of paper which is developed by means of different color developers, liquid development results in superposition of multicolored images.

A liquid developer generally comprises fine charged particles of a single polarity, which are suspended in a carrier liquid having high degree of electrical insulating properties. The most important requirement for a liquid developer is that for the amount and polarity of the charges on the fine particles that the liquid developer remain stable over a long period of storage.

Many conventional yellow pigments, such as benzidine yellow, lead chromate and Hansa Yellow, etc., are known,

hired States Patent 3,597,368 Patented Aug. 3, 1971 but all of them reveal some defects when used as a toner in a liquid developer for the development of a latent electrostatic image. That is, benzidine yellow G (CI. 21095) represented by the following formula shows an unstable charge retention which can be charged negatively when dispersed in an insulative liquid Also, even if resinous coatings which are conventionally known as a means for charge control of dispersed particles is applied, the tendency to negative charging still appears when the particles are stored over an extended period.

On the other hand, benzidine yellow GR (CI. 21100) prepared by introducing CH radicals into the p-position of a benzene nuclei at the opposite ends of the above formula shows an improved property in respect of the charge condition, but has an undesirable hue due to increased absorption in the green region of spectrum. Hansa Yellow, another conventional dye, lacks transparency and where it is desired to obtain a multicolor image by over print development as described above, the underlying color is apt to be concealed. The conventional dye lead chromate has the defect that it is apt to be charged negatively and also lacks transparency. As already known from the triboelectric charging characteristics of substances and also as from the charging characteristics in an insulative liquid, a substance containing a substitution radical like NO or Cl-- is apt to acquire a negative charge. Accordingly, the undesirable properties of a compound like benzidine yellow G is considered originating .in the presence of Clradical in the structural formula, but if a CH radical or a OCH radical is introduced in place of Cl, the absorption shifts to a longer wavelength, imparting an orange to orange red appearance in the resulting compound. Therefore, such countermeasures have not proved to be effective.

SUMMARY OF THE INVENTION The present inventors have now found that compounds having the following structural formulas possess especially desirable characteristics as dispersed tone particles in a In the above formulas, R represents a OCH OC H or a OC H radical.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The pigment according to the present invention has several prominent features over the conventional yellow pigments in that it has almost ideal absorption characteristics. Its dispersion in many insulative liquids is easy and stable and its electrophoretic properties therein are stable. Similarly, satisfactory results can also be obtained even if resins, or oils were mixed in liquids to facilitate dispersion and to regulate the electrophoretic characteristics. Especially, when the above compounds are employed, it is simple to obtain extremely fine particles which can produce a developed image of excellent transparency so that when a yellow image comprising this pigment is superimposed on top of the images already developed, for instance, by means of cyan and magenta developers, complete mixing of color is realized Without concealing the underlying colors.

The compound having a structure represented by the general Formula 1 or 2, for instance, in the case Where R is OCH can be obtained by the coupling of a tetrazotized product of 3,3-dichlorobenzene with O-anisidine acetoacetic acid which, in turn is synthesized from O-anisidine and acetoacetic acid ester.

The pigments according to the present invention have an intense tendency of acquiring charges of positive polarity and therefore, even if they were mixed, for instance, with a small quantity of another pigment having a similar structure and possessing an ambiguous charging characteristic, the developing characteristics will remain stable.

Mixtures of the pigments developed by the present in- I vention can, of course, be used as toners for liquid developers by being dispersed into an insulating liquid.

With more than 50% of a pigment composition of the present invention, the toner showed stable electrophoretic properties.

As examples of resins applicable for the preparation of liquid developers one can enumerate rosin-modified phenol formaldehyde resin, pentaerythritol ester of rosin, glycerin ester of hydrogenated rosin, ethylcellulose, various alkyd resins, polyacrylic or polymethacrylic resin, polystyrene, polyketone resin and polyvinyl acetate, etc. As for the carrier liquid of the liquid developer, aliphatic or alicyclic hydrocarbons such as cyclohexane, kerosene etc. and halogen-substituted saturated hydrocarbons, especially hydrocarbons containing fluorine are applicable.

Further, a trace of dispersing agents, surface active agents or vegetable oils can also be incorporated into the liquid developer.

The present invention relates to a novel developer providing a yellow image, whereby the positive charges are stably maintained. Therefore, if it is applied to an electrically negative latent electrostatic image, the attractive deposition under the action of Coulombs forces takes place. When applied to an electrically positive latent image, repulsion development occurs.

The developer of the present invention has one advantage that it can provide an especially excellent image in transparencies and therefore, when obtaining a multicolor image, it demonstrates excellent color reproducibility.

EXAMPLES (1) To 30 parts of a yellow pigment synthesized by the synthesis process described above and having the following structure were added 50 parts of rosin-modified phenolformaldehyde resin, 20 parts linseed oil and a proper quantity of aliphatic hydrocarbon solvent. The mixture was fully kneaded by means ofa three roll blender. One part of the paste thus obtained was dispersed in 1,000

parts of mixed solvent of cyclohexane and kerosene by means of an ultrasonlc dispersion device.

CH3 0 CH 1 A zinc oxide light sensitive paper bearing an electrically negative electrostatic latent image was processed with this developer and satisfactory developmentwas carried out, resulting in a background free image of high resolution. This pigment, holding positive charges in the liquid, has demonstrated a stable developing characteristic. even after storage over an extended period of time.

(2) A zinc oxide paper having sensitivity over the en-' tire range of the visible spectrum was charged negatively and exposed to a light image transmitting a lantern color slide (positive) combined with a red filter. It wasthen developed by means of a cyan liquid developer, after which it was recharged, exposed using the same slide combined with a green filter, developed by means of a magenta liquid developer, and finally, after exposure through a blue filter in a similar manner, developed using the developer men tioned in the Example 1. As a result of this procedure, a satisfactory color positive image could be reproduced.

The yellow pigment, being transparent, did not cause a trailing tendency in and around the developed image and also produced very little interference background.

What is claimed is:

1. A liquid developer for developing a latent electrostatic image containing fine particles comprising at'least 0;16 of the compounds selected from the group consisting o H ll wherein R is selected from the group consisting of OCH OC H and OC H as the main constituent thereof, which is positively charged and which is suspended in an electrically insulative liquid selected from the group consist: ing of aliphatic hydrocarbons, alicyclic hydrocarbons and halogen-substituted saturated hydrocarbons.

2. The developer as claimed in claim 1 wherein R is 0011 3. The developer as claimed in claim 2 wherein the fine particles are coated with rosin modified phenol-formaldehyde resin.

6 4. The developer as claimed in claim 1 wherein R is References Cited OC H 5. The developer as claimed in claim 1 wherein R is UNITED STATES PATENTS OC H 3,361,736 1/1968 Rlbba 260-176 6. The developer as claimed in claim 1 wherein said 5 3,105,321 10/1963 Johllsoll 252-421 electrically insulative liquid is an aliphatic hydrocarbon. 3,053,688 9/1962 'Grelg 7. The developer as claimed in claim 1 wherein said 2,361,569 10/ 1944 Reynolds 260-476 insulative liquid is an alicyclic hydrocarbon.

8. The developer as claimed in claim 1 wherein said GEORGE LESMES Pnmary Exammer insulative liquid is a halogen-substituted saturated hydro- 10 J, P, BRAMMER, Assistant Examiner carbon.

9. The developer as claimed in claim 8 wherein said US. Cl. X.R. halogen is fluorine. 260l76 

